1. Technical Field
The present invention relates to an image reading technique using an ADF (Auto Document Feeder) function.
2. Related Art
Image scanners (image reading apparatuses) are known which have the ADF (Auto Document Feeder) function. In such scanners, the entire image of the original document is read by a stationary image sensor while the original document is moved at a constant speed (for example, JP-A-2006-20084).
The image scanners temporarily store the read image data in a buffer, and sequentially transmit the data to a host such as a personal computer (PC). The transmission speed is determined in accordance with processing capability of the host computer. Hence, the reading speed of the image scanner is adjusted to a low speed which does not result in the buffer being filled up.
However, there is a demand for an increase in reading speed, but if the reading speed is high, the buffer tends to fill up. In this point, when the buffer is nearly full, a method can be considered in which the sheet feeding of the original document is temporarily stopped.
However, when a sheet feeding roller of a sheet feeding device is driven at a speed above a predetermined speed, sudden stopping may not be possible in terms of mechanical structure. Thus, a deceleration step is required. Further, when the sheet feeding roller of the sheet feeding device is driven at the speed above the predetermined speed, it may not be possible in terms of mechanical structure to suddenly drive the roller at high speed. Thus, an acceleration step is required.
In existing image scanners, the acceleration step and the deceleration step are not considered. If the acceleration step and the deceleration step are provided, distortions occur in the read image.